NS 248 is an introduction to the principles and practice of epidemiology and the use of data in program planning and policy development. The course covers the major concepts usually found in a graduate-level introductory course in epidemiology: outbreak investigations, study design, measures of effect, internal and external validity, reliability, and causal inference. Assigned readings are drawn from a standard textbook and the primary literature. In addition, students read case studies and work step-by-step through major epidemiologic investigations of the past century; they also form small groups to design and conduct a small epidemiologic study on campus. The major assignments are four case studies, regular response papers/worksheets on the readings, a critique of a primary paper, a poster presentation of the on-campus study, and a proposal for an epidemiologic study of their own design.